1. Field of the Invention
This invention relates to containers for a photographic film cartridge.
2. Description of the Prior Art
A common photographic film cartridge is shown in FIG. 26. A photographic film is wound around a spool 16 made of plastic resin, and placed in the cartridge body 18. The cartridge is well known as a JIS 135 type cartridge, and light-shielding members called teremp cloth are attached to the exit slit of the cartridge body 18 (e.g. Japanese Utility Model KOKOKU No. 41-6297). The leading end of the photographic film is called a tongue 17. Various improvements have been made with respect to the exit light-shielding structure (e.g. Japanese Patent KOKOKU No. 43-3416, Japanese Utility Model KOKOKU No. 37-32164). Improvements in the cartridge body 18 have also been made, and a cartridge body made of a plastic resin was proposed for the purpose of reducing weight (Japanese Patent KOKAI No. 55-21089).
The photographic film cartridge is placed, for example, in a container shown in FIG. 1. The container consists of a container body 1 and a cap 2 fitted thereto. The container body 1 is formed of a cylindrical shape having a bottom composed of a bottom portion 3 and a peripheral wall portion 4. An annular fitting groove 5 is formed near the upper edge on the inside of the peripheral wall portion 4, and an annular projection 6 to be fitted into the groove 5 is formed on the container cap 2. A semispherical recess 12 is formed at the bottom portion 3, and a projection of gate mark portion 9 remains therein. Some other container bodies are illustrated in FIGS. 4 through 8. Such a container body is produced by injection molding. That is, a melted resin is injected into a mold through the gate portion 10, and after solidified by cooling, it is taken out of the mold. In the case of container bodies for a photographic film cartridge, since a great quantity is mass-produced, a multi-cavity mold is used in a hot runner type, and the container bodies are molded at a high speed.
The present inventor has investigated in order to improve containers for photographic film cartridges, and has disclosed a container body made of a polypropylene resin having a propylene unit content of more than 70 wt. %, a melt index (ASTM D-1238) of 16 to 80 g/10 minutes, a yielding point of tensile stress of higher than 250 kg/cm.sup.2, a bending elastic modulus of higher than 10,000 kg/cm.sup.2 and a notched Izod impact strength of higher than 2.0 kg.multidot.cm/cm containing an organic nucleating agent (U.S. Pat. No. 4,639,386), a container body made of a particular polypropylene resin containing a fatty amide lubricant (Japanese Patent KOKAI No. 61-73947), a container body made of a resin composed of 60 to 99.9 wt. % of a particular polypropylene resin, 0 to 39.9 wt. % of polyethylene or ethylene copolymer resin and 0.1 to 15 wt. % of aluminum powder or aluminum paste (Japanese Patent KOKAI No. 61-250639), and a container body made of a resin containing a propylene-ethylene random copolymer composed of 95 to 99 wt. % of propylene units and 1.5 to 4 wt. % of ethylene units having a melt index (MI) of 10 to 70 g/10 minutes and a molecular weight distribution of 2.5 to 5.5 and containing an organic nucleating agent (Japanese Patent Application No. 63-158985).
In the case of the above conventional container for a photographic film cartridge, white powder occasionally adhered to the leading end of the photographic film, the teremp cloth attached to the exit slit of the cartridge or like during the physical distribution. The white powder gave unnecessary uncertainty to users and sometimes affected adversely photographic properties of the film.
The conventional container body for a photographic film cartridge has a sufficient impact strength. However, deformation of the opening, buckling and the like are liable to occur. When additives were increased in order to solve these problems, the additives bled to increase white powder generation. In the case of container bodies made of homopolypropylene resin, since the rigidity is made great, deformation of the opening, buckling and the like can be prevented. However, the impact strength is weak, and cracking is liable to occur by dropping.
Another problem of a conventional container body was in the occurrence of a bottom sink mark and buckling at the time of taking the container bodies out of their molds. The inventor found that the bottom sink mark and buckling occurred caused by the formation of a vacuum due to the smooth inner surface of the peripheral wall portion. Thereupon, the inventor devised a container body for a photographic film cartridge wherein at least more than one third from the bottom of the inner surface is made a rough face having at least 7 .mu.m in depth (Japanese Patent KOKAI No. 63-193142). The roughed container body can be taken out of the core of the mold without the occurrence of a bottom sink mark and buckling. Incidentally, since a great deal of containers for a photographic film cartridge are produced, to decrease the resin quantity is very important.
Another problem is in that, when container bodies for a photographic film cartridge are molded by injection molding using a polyolefin resin having a MI of 10 to 60 g/10 minutes, particularly a propylene-.alpha.-olefin copolymer containing more than 0.5 wt. % of .alpha.-olefin at a high speed molding of less than 12 seconds/cycle using a multicavity mold of more than 16 cavities in a hot runner type, the gate mark portion 9 is occasionally scraped upon removal from the mold caused by uneven cooling. As a result, pinholes or a thin portion is produced which generates a problem in moistureproofness, and visual inspection is necessary.